Tropical Trouble: Species to Struggle in Heat

by Andrea Thompson | May 05, 2008 01:00pm ET

Polar bears may be the poster children for the havoc that climate
change could wreak on sensitive species, but animals and plants in the
tropics could actually be in the greatest peril from global warming, a
new study suggests.

While temperature changes in the tropics are expected to be much less extreme than those at higher latitudes,
tropical species actually have a far greater risk of extinction from
just a degree or two of warming, according to the results of the study,
detailed in the May 5 issue of the journal Proceedings of the National Academy of Sciences.

Tropical species are accustomed to living within a much smaller
temperature range than species at temperate and higher latitudes, so
once temperatures exceed that range, many hot-zone species might not be
able to cope, the authors said.

"There's a strong relationship between your physiology and the
climate you live in," said study team member Joshua Tewksbury of the
University of Washington. "In the tropics many species appear to be
living at or near their thermal optimum, a temperature that lets them
thrive. But once temperature gets above the thermal optimum, fitness
levels most likely decline quickly and there may not be much they can
do about it."

This threat to tropical species is particularly worrisome because, "unfortunately, the tropics also hold the large majority of species on the planet," said study team member Curtis Deutsch of the University of California, Los Angeles.

Tewksbury and Deutsch, who was a postdoctoral researcher at UW when
the study was done, took temperature records from 1950 to 2000 and
climate model projections from the Intergovernmental Panel on Climate
Change for the first years of the 21st century and compared them to
data describing the relationship between temperature and fitness for a
variety of temperate and tropical species, including insects, frogs,
lizards and turtles. Their research was funded in part by the National
Science Foundation and the UW Program on Climate Change.

How a given species would fare in a warming world appeared to depend
more on how a temperature change would affect population levels and a
species' physical performance than the actual amount of warming
predicted for where they lived.

Some tropical species can now shield themselves from the heat of the
day by sitting under a shady leaf or burrowing into the soil. But if
they are already living close to their critical high temperature, a
slight increase in air temperature could make staying out of the sun a
futile exercise, Tewksbury said. Warming may simply come too fast for
the creatures to adapt.

Andrea Thompson

Andrea graduated from Georgia Tech with a B.S. in Earth and Atmospheric Sciences in 2004 and a Master's in the same subject in 2006. She attended the Science, Health and Environmental Reporting Program at New York University and graduated with a Master of Arts in 2006.